Calculating work from E-Field Graphs

[xSnoopy]

Homework Statement

a)Calculate the work performed by an external agent to move a charge of -0.39x10^-12 C from `i' to `b'

http://capa-new.colorado.edu/msuphysicslib/Graphics/Gtype54/prob04a_threeqcontour.gif

Hint: The equipotential lines shown are separated by 1 kV. Work to move a charge is the increase in potential energy of the charge. The potential energy is the potential times the charge.

b)Calculate the magnitude of the electric field at `k'.

Homework Equations

a)-q*ΔV = Work
b) E = -ΔV/Δd

The Attempt at a Solution

a)I have tried simply plugging in the values:
q = (-0.39x10^-12) and ΔV = ([3 - +3]*1000)

And got the answer 2.34*10^-9 J

b)not really sure where to start here...

 

[TSny]

Hi xSnoopy. Look at the equipotential lines plot and pick an appropriate interval of distance Δd. You'll need to decide where to choose the location of Δd and what direction to orient it. You can then use the ruler in the diagram to estimate Δd in centimeters. Decide how to use this to estimate E.